Boston and Dallas partnered in some risky business Thursday, with the Bruins dealing away a potential superstar in Tyler Seguin, and the Stars shipping out a known, prime-aged, proven scorer in right wing Loui Eriksson.

Whose risk is greater? No doubt that falls to Boston, because Seguin is only 21, is among the game’s fastest skaters, and really never was given the opportunity to prove himself at center, his natural position, which was how he projected in the NHL when the Bruins made him the No. 2 overall pick in the 2010 draft.

But here’s the thing about Seguin: The Bruins stopped believing he could be a bona fide NHL No. 1 pivot. They began to wonder if he had the toughness and temerity and hockey IQ to play effectively among the top six forwards in their north-south, tough-to-play-against, “Bruins style” of hockey. General manager Peter Chiarelli also acknowledged Thursday what he has seen in the “Twitterverse’’ about Seguin, “a lot of reports about extracurricular stuff.’’

So bundle up the doubts, the clinical read, the innuendo, and the hearsay, and the Bruins decided to say so long to the potential phenom. Sound rash? Well, they had 36 months to live with him, preach their game, tell him what they expected out of him shift to shift, and how they expected him to act when he was away from the rink.

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Three years, three seasons, and they finally drew the line, which was quite obvious last Sunday when Chiarelli noted at the draft in Newark that it was time for the promising young gun to button down and be a pro. GMs don’t hurl wunderkinds under buses without cause, especially not Peter The Patient, quite possibly the most reserved of the league’s 30 GMs.

Now, let it be duly noted that Chiarelli is also the guy who dropped nearly $35 million in Seguin’s lap last summer in the form of a six-year contract that kicks in this October. That financial promise, in tandem with the doubts, clinical analysis, innuendo, and hearsay was no doubt the tipping point in finding Seguin a new home.

The deal last summer made Seguin a made man, well ahead of him becoming a man in this child’s game of hockey. As I noted in this space last Wednesday, less than 48 hours after the Bruins were eliminated in the Stanley Cup Final, it behooved Chiarelli to investigate trade possibilities for Seguin now, or run the risk that another underwhelming season in 2013-14 would make it all the harder to find a trade partner this time next season.

Seguin’s cap hit, $5.75 million, had the potential of turning into an immovable white elephant if his production flatlined or dipped in his fourth NHL season. He did not get better in the shortened 48-game regular season, and under the heat of a 22-game playoff run, he actually got worse. All said and done, he was a third-line right wing with limited effectiveness (22 games, 1-7—8) the night the Blackhawks sashayed down Causeway Street with the Cup.

Meanwhile, Eriksson will be 28 later this month and there is no doubting what he is or who he is. He is the quintessential low-maintenance, plug-in, dress-and-aim scorer (left shot/right wing) who averaged roughly 30 goals and 70 points across the four seasons leading to this past season’s lockout. All for an undertalented Dallas squad that failed to make the playoffs in all four of those seasons. All the while providing smart two-way play and rarely missing a game. Since October 2008, in fact, he missed but three games, in 2010-11, and otherwise answered the bell every night.

Think of Eriksson this way: He’s Patrice Bergeron with greater scoring touch, playing on the wing instead of in the middle. For a cap hit of $4.25 million on a deal that runs three more seasons. The Bruins haven’t had a regular 30-40—70 guy on the wing for about 10 years, when Glen Murray was cashing in Joe Thornton’s dishes.

The maraschino cherry is that Chiarelli also moved a fast-fading Rich Peverley, who had two years left on his deal with a $3.25 million cap hit. In one trade, Chiarelli deleted $41 million in cap committment and took back only Eriksson’s $12.75 million, for a net savings of $28.2 million. The break on the upcoming 2013-14 cap is $4.75 million, a portion of which Chiarelli will stuff in an offer Friday when he officially tries to woo Daniel Alfredsson away from the Senators. If he fails to land Alfredsson, it’s money he can spend on someone else, or use to ease some of the huge pay increase free agent goalie Tuukka Rask is about to receive.

Now, back to the Bruins’ risk. No one is saying Seguin can’t or won’t get serious about how to apply his obvious, abundant talents. He’s young, and history shows very few newbies arrive with the game and adult demeanor/finish of the likes of, say, Ray Bourque, Chris Drury or Alfredsson, just to name three. Let’s also not forget that some arrive with the adult thing nailed, such as Sergei Samsonov, and then disappear into age 20-something obscurity. Samsonov was the league’s 1998 Rookie of the Year with the Bruins and that ended up being his career highlight.

A lot of US college hockey players are advancing to their senior season at age 21, and Seguin has 121 NHL points as a headstart on all of them. He also has the reality slap of Thursday’s trade. It could be the slap that puts his game back on that trajectory of being a No. 1 center.

Bruins fans have seen how this can unfold over time. Rick Middleton, the No. 14 overall pick by the Rangers in 1973, played two unremarkable seasons on Broadway before he was dealt to Boston at age 22. He became a huge star in the Hub and remains one of the game’s top talents not to be inducted into the Hockey Hall of Fame. Oh, the negligence of the induction committee.

In the 1983 draft, the Canucks selected Cam Neely No. 9 overall. He sat virtually at the end of the bench for three seasons until Vancouver dealt him to the Bruins at age 21 in the summer of ’86. He is now the Bruins’ president with a Hall of Fame curriculum vitae that reads 726 games, 395 goals and 694 points.

Personally, I doubt Seguin’s career comes close to those of Middleton or Neely. Both played with the focus, intensity, intelligence, courage, and unflappability with the puck that Seguin has yet to demonstrate. He could get there. He may get there. Some even will argue that he should get there.

But just as the Rangers ran out of patience with Middleton, and the Canucks with Neely, it ran out here for the Bruins with Seguin. His game had holes. Management had questions and a few reservations. On top of it all, he was promised paychecks totaling $34.5 million over the next six years. It didn’t have to end this way, but it’s no surprise that it did.

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